Purchase an Atari 850 Interface Module (15-30 mins)

Task: Purchase an Atari 850 Interface Module

Needed: Web browser

Time: 15-30 minutes


The Atari Serial Input/Ouput System or SIO was designed to allow the computer to communicate with peripherals such as the 810 or 1050 disk drive. An advantage of the SIO is that multiple devices could be chained together. A major design consideration was allowing the Atari computer to communicate with peripherals without the need for installing an internal card. Unfortunately, a number of devices such as third-party printers used a different communication port called an RS-232. Atari made the 850 Interface Module to allow communication with devices that used the RS-232 port. The figure below was taken from the 850 user’s manual and shows an example setup with both SIO and RS-232 devices connected to the computer.

Example 850 Setup
Example 850 Setup

These are still somewhat useful today as printers and modems (e.g. modern wifi modems) often use the RS-232 port. Fortunately, they are relatively easy to come across on eBay and other sources.


The 850 Interface Module can be easily found on eBay for around $50 to $75. At the time of this posting there were about six available and most were listed for $50.

Atari 850 Interface Module
Atari 850 Interface Module


I have seen some criticism of the 850 but I think it has been a useful device to have. I still have mine from back in the day and acquired a second as part of a lot I picked up locally. My only beef with the 850 is the design. I would have been thrilled if the 850 could have sat sandwiched between my 810 disk drive and my 820 printer with the same form factor. Unfortunately, the footprint of the 850 is smaller than the 810 which means it needs to sit on your desk somewhere. I find this awkward. Also, it is very lightweight which means it doesn’t stay where you put it. Another design question is why Atari didn’t release one in the style of the XL and then XE series? The Atari FAQ has a lot of information about this peripheral (see Section 6.1.1).